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TT: Fachverband Tiefe Temperaturen

TT 50: Superconductivity: Theory II

TT 50.9: Vortrag

Mittwoch, 20. März 2024, 17:15–17:30, H 3005

Splitting of d-wave surface states: Edge ferromagnetism or spontaneous supercurrents? — •Kevin Marc Seja, Niclas Wall-Wennerdal, Tomas Löfwander, and Mikael Fogelström — MC2 - Microtechnology & Nanoscience, Chalmers University of Technology, Gothenburg, Sweden

At pair-breaking surfaces of a d-wave superconducting grain, Andreev bound states appear in the middle of the superconducting energy gap. The resulting large density of states at zero energy is energetically highly unfavorable. Experimentally, the associated tunneling-conductance peak was found to split spontaneously into two finite-energy peaks at low temperatures[1]. Two suggested mechanisms for this are either ferromagnetic interaction at the surfaces[2], or the establishment of phase gradients in the order parameter[3]. It is an open question which of the two cases minimizes the free energy at finite temperatures. Here we present a theoretical study of this problem using the quasiclassical theory of superconductivity. We include a magnetic Fermi liquid interaction, allow for a complex order parameter, and solve the underlying transport and self-energy equations selfconsistently in 2D by finite element method[4]. Depending on interaction strength and temperature, we find either a first-order transition to a purely magnetic or a second-order transition to a current-carrying state. We discuss key differences between the two phases.

[1] Covington et al., Phys. Rev. Lett. 79 (1997) 277

[2] Potter & Lee - Phys. Rev. Lett. 112 (2014) 117002

[3] Håkansson et al., Nat. Phys. 11 (2015) 755

[4] Seja & Löfwander - Phys. Rev. B 106 (2022) 144511

Keywords: d-wave; Andreev bound states; Quasiclassical theory; Phase transition; unconventional superconductors